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Date:   Mon, 2 Jan 2023 20:20:11 -0800
From:   Ira Weiny <ira.weiny@intel.com>
To:     Jan Kara <jack@suse.cz>
CC:     "Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
        Jan Kara <jack@suse.com>, <linux-ext4@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH] fs/ext2: Replace kmap_atomic() with kmap_local_page()
Message-ID: <Y7Os+9kkU9Scnfss@iweiny-mobl>
References: <20221231174205.8492-1-fmdefrancesco@gmail.com>
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On Mon, Jan 02, 2023 at 01:34:11PM +0100, Jan Kara wrote:
> On Sat 31-12-22 18:42:05, Fabio M. De Francesco wrote:
> > kmap_atomic() is deprecated in favor of kmap_local_page(). Therefore,
> > replace kmap_atomic() with kmap_local_page().
> > 
> > kmap_atomic() is implemented like a kmap_local_page() which also disables
> > page-faults and preemption (the latter only for !PREEMPT_RT kernels).
> > 
> > However, the code within the mapping and un-mapping in ext2_make_empty()
> > does not depend on the above-mentioned side effects.
> > 
> > Therefore, a mere replacement of the old API with the new one is all it
> > is required (i.e., there is no need to explicitly add any calls to
> > pagefault_disable() and/or preempt_disable()).
> > 
> > Suggested-by: Ira Weiny <ira.weiny@intel.com>
> > Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> 
> Thanks, the patch looks good and I'll queue it in my tree. I'm not sure why
> it got missed during the initial conversion by Ira :).
> 

I could claim something smart like I was focused on kmap() calls only.  But
let's just call it laziness.  ;-)

LGTM

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

> 								Honza
> 
> 
> > ---
> > 
> > I tried my best to understand the code within mapping and un-mapping.
> > However, I'm not an expert. Therefore, although I'm pretty confident, I
> > cannot be 100% sure that the code between the mapping and the un-mapping
> > does not depend on pagefault_disable() and/or preempt_disable().
> > 
> > Unfortunately, I cannot currently test this changes to check the
> > above-mentioned assumptions. However, if I'm required to do the tests
> > with (x)fstests, I have no problems with doing them in the next days.
> > 
> > If so, I'll test in a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel with
> > HIGHMEM64GB enabled.
> > 
> > I'd like to hear whether or not the maintainers require these tests
> > and/or other tests.
> > 
> >  fs/ext2/dir.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/ext2/dir.c b/fs/ext2/dir.c
> > index e5cbc27ba459..0f144c5c7861 100644
> > --- a/fs/ext2/dir.c
> > +++ b/fs/ext2/dir.c
> > @@ -646,7 +646,7 @@ int ext2_make_empty(struct inode *inode, struct inode *parent)
> >  		unlock_page(page);
> >  		goto fail;
> >  	}
> > -	kaddr = kmap_atomic(page);
> > +	kaddr = kmap_local_page(page);
> >  	memset(kaddr, 0, chunk_size);
> >  	de = (struct ext2_dir_entry_2 *)kaddr;
> >  	de->name_len = 1;
> > @@ -661,7 +661,7 @@ int ext2_make_empty(struct inode *inode, struct inode *parent)
> >  	de->inode = cpu_to_le32(parent->i_ino);
> >  	memcpy (de->name, "..\0", 4);
> >  	ext2_set_de_type (de, inode);
> > -	kunmap_atomic(kaddr);
> > +	kunmap_local(kaddr);
> >  	ext2_commit_chunk(page, 0, chunk_size);
> >  	err = ext2_handle_dirsync(inode);
> >  fail:
> > -- 
> > 2.39.0
> > 
> -- 
> Jan Kara <jack@suse.com>
> SUSE Labs, CR